There are two things that should be note about copyright, which would have prevented AT&T or anyone else from actually enforcing any copyright on such simple files.
First, copyright does not protect ideas--it only protects the way an author expressed the idea. The closer the expression is to the minimal way to express the idea, the less likely it is to be copyrightable. In the case of the simple implementations of /bin/true and /bin/false, they are pretty darned close to minimal.
Second, if you have author X who produces a copyrightable work, and author Y who later independently produces a work that happens to be identical to X's work, but Y did not copy elements from X, Y is not infringing X's copyright.
This second case doesn't happen often. If someone were to decide to write a novel about boy wizards, and produced something identical to the first Harry Potter book, no one would believe that they did this without copying from Rowling. However, if the work is small enough, an identical independent work is believable.
In the case of the simple /bin/true and /bin/false, a defense that you didn't copy from AT&T would be believable. Even if you admitted you looked at the AT&T source or had it described to you, it would be believable that you produced your own expression of the idea of "a do nothing shell script" and a "shell script that exits with status 255".
For comparison, here is /usr/bin/false from my Solaris box:
$ cat /usr/bin/false
#!/usr/bin/sh
# Copyright (c) 1984, 1986, 1987, 1988, 1989 AT&T
# All Rights Reserved
# THIS IS UNPUBLISHED PROPRIETARY SOURCE CODE OF AT&T
# The copyright notice above does not evidence any
# actual or intended publication of such source code.
#ident "@(#)false.sh 1.6 93/01/11 SMI" /* SVr4.0 1.3 */
exit 255
Did AT&T actually tried to enforce this copyright? Because what I see is auto-generated header that is put to every shell script present on the system. Entertaining nonetheless.
After the "insert copyright headers in all files" edict is given, it isn't unusual to find empty files that are copyrighted. Config files placeholders in particular end up copyrighting the zero length file.
I worked at a company that didn't merely issue this edict, but attempted to enforce it technologically. Every file in every commit was checked for the presence of a prescribed style of copyright string (something along the lines of "Copyright (c) YYYY Acme Inc.").
For a lot of my time there, I was more operations than development. A lot of piddly-ass configuration files and other things no copyright could possibly exist for got copyright strings added just so I wouldn't have to remember to type "NO ACME COPYRIGHT" into every bloody commit message to bypass the hook.
One of the issues in the AT&T versus UC BSD lawsuit was that AT&T forgot to copyright many of their files. (This was before automatic copyright.) So they probably over-reacted and went out of the way to label everything.
That's the C runtime starting up and finishing. That amount of overhead is incurred by (nearly) any program; in fact, worse overhead is incurred using the Sun method of having an empty file, because you have to run the more complex /bin/sh (or equivalent) instead of just a trivial compiled program.
ltrace gives a better view of what the program itself (as opposed to the runtime) is doing.
This is GNU's Appropriate Legal Notices as required by section 5d of the GPLv3:
An interactive user interface displays "Appropriate Legal Notices"
to the extent that it includes a convenient and prominently visible
feature that (1) displays an appropriate copyright notice, and (2)
tells the user that there is no warranty for the work (except to the
extent that warranties are provided), that licensees may convey the
work under this License, and how to view a copy of this License. If
the interface presents a list of user commands or options, such as a
menu, a prominent item in the list meets this criterion.
How can we know? A mere veiled threat of litigation is enough to make a lot of corporations cower in fear, and stop doing whatever generated the threat. Does merely threatening a suit constitute "enforcing the copyright"?
As many know the #ident tag in 'C' code was used with SCCS (pre-cursor to git/svn/cvs/etc) to create a string in the 'binary' which identified the code. In shell scripts it just sat there.
The change in the ident string where it gets the 'SMI' is when the version was from 'Sun Microsystems Inc' (aka SMI).
The reason Solaris included it was because it was part of the 'merge' between SunOS and System V and Sun had permission to all of the AT&T copyrights with respect to UNIX once they became 'partners' (AT&T invested essentially a billion dollars in Sun).
I think I remember an engineer I worked with in the past gleefully pointing to a preface page in an Intel handbook for a chip Intel designed that Intel had copyrighted the lowercase letter i.
